The compression of CO2-rich and wet streams requires the use of a compressor made of stainless steel—or even made of materials that are more noble still, such as steels that have a high nickel content—in order to prevent corrosion by carbonic acid, or by other stronger acids that might result from the presence of impurities in the CO2-rich stream, such as nitrogen oxides or sulfur oxides.
A CO2-rich fluid contains between 1 mol % and 100 mol % of CO2 on a dry basis. Ambient air is 25 times more depleted in CO2 than the bottom limit of 1 mol %.
It is in this way that the prior art for the treatment of such CO2-rich streams is schematically represented, as in FIG. 1.                1=provision of the CO2-rich stream (examples: outlet of a column for regenerating a solvent (amine type) or oxycombustion flue gases after a primary filter of electrostatic or bag filter type        3=optional step of fine purification (to a typical level of the order of 1 part per million) of sulfur-containing elements        5=compression in a compressor, the materials of which in contact with the wet gas are made of corrosion-resistant steel        7=drying of the gas by adsorption (for example adsorbent of activated alumina, molecular sieve or silica gel type)        9=optionally purifying the CO2-rich gas of its light constituents (oxygen, argon, hydrogen, carbon monoxide, nitrogen, etc.) and/or of its heavier constituents (NO2, N2O4, SO2, etc.), the possible variants of this step are described at length in previous patent applications;        11=step of compression of the CO2-rich final product or of liquefaction of the CO2-rich final product in order to make it available to a system of transport (by pipeline or boat) or for its use in a process.        
It is known from U.S. Pat. No. 2,862,819 to separate a stream of CO2-rich gas by distillation, after having mixed it with an antifreeze before compressing it in a compressor.